JPS6287137A - X-ray ct apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an X-ray CT apparatus that performs a spiral scan.

[Background of the invention]

An X-ray CT apparatus is a device that irradiates a subject with X-rays to obtain a tomographic image of the subject. When photographing continuous slices (LIFR layer planes) with an X-ray CT device, a spear blade is used to irradiate each slice plane with X-rays individually. To do this, the ped carrying the subject is moved forward (or backward) in fixed pitch units, and the X#5, which is controlled separately from the ped, is
! The tomographic plane is irradiated with Xs from the source at each pitch. The transmitted X-rays obtained for each pitch are received by an X-ray detector, the detection signal obtained by the X-ray detector is subjected to t-AD conversion, and then data processing and image reconstruction are performed.

In this way, a tomographic image on one slice plane is obtained for each pitch.

Although the purpose of this method is to obtain tomographic images in continuous slices, the actual tomographic images are in discontinuous slice planes. This is because the ped is advanced at a fixed pitch and an image is taken each time.

Obtaining tomographic images in continuous slices is essential for obtaining accurate diagnosis at the diagnosis site. - If the movement pitch is reduced, it would be possible to obtain tomographic images in pseudo continuous slices, but it would take a long time to capture the entire image.

[Purpose of the invention]

An object of the present invention is to provide an X-ray CT apparatus that is capable of obtaining continuous tomographic images by continuous slices.

[Summary of the invention]

The present invention moves the ped carrying the subject (forward or backward) while continuously irradiating X-rays in the circumferential direction.
I decided to let him do it. This movement causes an X-ray scan to be performed on the subject in a spiral manner. The X-ray transmission data obtained by this spiral X-ray scan is converted into X-ray transmission data on each slice plane by interpolation, and then image reconstruction is performed to obtain a tomographic image.

[Embodiments of the invention]

FIG. 2 is an external view of the RR type CT apparatus.

The X-ray CT device consists of an X-ray tube device (X-ray generator) 1 and an
It consists of a ray detector 2, a high voltage generator for an X-ray tube (not shown), and a patient ped 3. The X-ray tube device 1 and the X-ray detector 2 are positioned opposite to each other with the subject on the ped 3 interposed between them. Under this opposing positional relationship, the X-ray tube [1 and
The line detector 2 is continuously rotated. For continuous rotation,
Is the high voltage from the high voltage device to the X-ray tube device 1 a slip ring? Power was supplied through the

The X,93 tube device 1 and the X-ray detector 2 are integrally mounted on the frame. A slip ring mechanism is attached to the frame (scanner) to supply high voltage.

, the patient bed 3 can be moved at a constant speed in a direction (arrow) perpendicular to the plane of rotation of the scanner. Moving patient bed 3 and X
The radiation of X-rays by the ray tube device 1 and the rotation of the X-ray tube device 1 are synchronized with each other.

Now, the scanner rotates continuously and at high speed in a fixed rotation plane. At this time, the patient bed 3 is inserted into the entry opening 4 at a constant speed, and a range including the desired tomographic plane is scanned. Prior to this scanning, scanning positioning is performed.

For positioning, as shown in FIG.
is positioned. The distance a provides a margin for the movement speed of the patient ped to become constant, and after the scanner and patient bed start rotating and moving, the XWMA pulse is adjusted in synchronization with the B plane (distance b) where the speed becomes a steady state. Start firing.

In this case, the distance is a distance for which extra data must be measured at the beginning and end of measurement TH, since projection data is obtained using interpolation in the direction in which the patient bed moves. The patient bed has passed the final fault plane 7 by the distance 8
When reaching the 7th plane, the X-ray radiation is stopped, and the patient bed decelerates and stops at the A' plane. In this way, by moving the patient bed during the scan, as seen from a stationary subject,
The image is scanned in a spiral manner as shown in FIG. 4(a). FIG. 5 shows the trajectory of the X-ray tube device relative to the subject at this time.

The projection data obtained by spiral scanning (hereinafter referred to as spiral data) is the projection data obtained when the scanner is rotated in a spiral around the subject and scanned, as shown in Figure 4. is equivalent to

The helical data SR is determined by the projection angle β and the position X of the subject in the body axis direction. Here, let X be the position at the start of scanning, and let D be the distance that the bed (and the subject) moves during one rotation of the scanner. To reconstruct the fault S (Xn), projection data R (β, xn) (β = 0° to 360°
)is necessary. The present invention is characterized in that projection data R of a desired tomographic plane is obtained from the Ra family data SR, and an image is reconstructed from the projection data.

To obtain a tomographic image, it is sufficient to obtain projection data on that tomographic plane.

Ra family data SR (β+, Xj) oo(β1≦360'
(1) X0≦Xj≦X6 (Scanning start position) (From the scanning start position, projection data R(
βI+Xゎ) X0+D(X.<X,-D(2
), position X, Nora family data SR (β, X,
), the projection data R(
β1. XrI) is determined by interpolation. Using two-point linear interpolation, if a = Xnll - Xn b = Xn - Xl, then R (β, Xn) = (SR (β, Xl) × a + 5
RCI3. Xm) x b l/(a+b) −(3
It can be found by 1. If this process is performed in all directions (all projection angles) of 360°, projection data at position Xn can be obtained.

Also, as shown clearly in Figure 5, 3 at position Xn
To obtain projection data in all directions of 60°, scanning is required in the range of Xn±D. Therefore, the scanning range is set to the position Xo−+
Assuming that X0, the projection data that can be obtained is at position X, as shown in (1) and +2). 10-X, -D
It is.

An embodiment of the X-ray CT apparatus of the present invention is shown in FIG.

The X-ray CT device consists of an X-ray generator 1. X-ray detector 2, data acquisition circuit 2, Parkfa memory 12, interpolation circuit 13,
Filter correction circuit 14, back projection calculation circuit 15, CRT
16.

X-ray generator 1: generates a fan-shaped X-ray beam; X-ray detector 2: consists of a multi-channel detection element that detects a transmitted fan-shaped x5 beam.

Data acquisition circuit 2 people...Multi-channel X-ray detector 2
The detected values are taken in and subjected to processing such as Griano and AD conversion to obtain helical projection data SR.

Two-dimensional buffer 12 is a buffer having i×j addresses. Stores helical projection data SR.

That is, this buffer 12 stores the projection number, scanner rotation speed (
It is determined by the number of rotations). Specifically, if the number of projections in one rotation of the scanner is pp, and the number of rotations of the scanner (how many scans have been performed) is JC, then the . It is required as follows.

however, ΔD=D/pp becomes.

Interpolation circuit 13: When a position Xn is specified, a projection r-R(1,X,) at Xn is created. That is, the helical projection data SR is converted into projection data R.

Filter correction circuit 14...Performs blur correction. The filter function is determined by the content of blur correction.

Back projection calculation circuit 15: Back projects the filtered output of the filter correction circuit 14. A tomographic image is thereby obtained.

CRT 16...Displays tomographic images.

Explain the operation.

The X-ray generator 1 and the X-ray detector 2 are continuously rotating on a predetermined plane. In this state, the bed 3 carrying the subject moves forward at a constant speed. X on the subject in the process of advancement
X-rays from the ray generator 1 are emitted. This exposure is performed by spiral scanning. Transmitted X-rays obtained by spiral scanning are detected by the X#J detector 2, and subjected to various preprocessing and AD conversion by two data acquisition circuits. In this way, spiral data SRi is obtained. This group data SR is stored in a two-dimensional buffer 12 whose addresses are arguments i and j. Similarly, the group data SR is obtained over the entire measurement range of the object and stored in the two-dimensional buffer 12.

After the two-dimensional buffer I2 is filled with the spiral data, the interpolation circuit 13 obtains the projection data Rt- of the desired tomographic plane from the spiral data SR. That is, the desired tomographic plane is specified by specifying the position Xrl, and the projection r-ta Rci, xn) at the position Xn is
Create. Specifically, as is clear from 2(41, +51), if the sample position of the spiral data SR in the body axis direction of the subject is taken as the horizontal axis and the projection number i is taken as the vertical axis, the relationship shown in Fig. 6 is obtained. Therefore, the projection data R(iTXn) can be obtained using the following formula.

R(1,X,)=(S R(l, Jl)x a
+ SR(1, J t+t)Xb )/(a+b)・
(6) Next, the obtained projection r-data R(i, Xn) undergoes blur correction processing in the filter correction circuit 14. The projection data after the blur correction process is subjected to back projection processing in a back projection calculation circuit 15,
A tomographic image at position tiTxn is obtained. CRT 16 displays a tomographic image.

Another example will be described. The patient bed is moved not only in one direction but also in the opposite direction to scan from plane B to plane B' in FIG. At this time, a trajectory 9 of forward movement and a trajectory 8 of backward movement
When scanning is performed so that the two intersect, the subject is scanned as shown in FIG. 4(b). When obtaining only one tomographic image and the seventh
This will be explained using figures (a) and (b).

FIG. 7(a) shows the scanner rotation speed 161. The relationship between the patient bed moving speed 17 and the X-ray radiation 18 is shown in a time chart. From Figure 7 (b), 180° (or more) is required to obtain one tomographic image.
The scanner performs another scan 9 in the forward direction.
After moving the patient bed until it rotates by 80 degrees, stopping the X-ray explosion, and shifting the phase by 180 degrees (by doing this, the forward and reverse trajectories intersect), the reverse direction 1c180' (or more) scans 8, the trajectory 9 of the X-ray tube device relative to the subject becomes as shown in FIG. 7(b). However, the dashed line indicates movement of the patient bed.
This indicates that only the scanner is rotating with the X-ray emission stopped.

When scanning in this manner, projection data is obtained by interpolating projection data when the patient bed is moving in the forward direction and projection data when the patient bed is moving in the reverse direction. Also,
In Example 1, the error due to interpolation was the same for any tomographic plane, but in Example 2, the error due to interpolation is the smallest on a plane that includes an intersection and is perpendicular to the bed movement direction. Therefore, when scanning as shown in FIG. 7(b), the tomographic plane 19
seek.

In FIG. 8, (a) is a projection of the trajectory from above, and (b) is a projection of the trajectory from the side. The tomographic plane 19 in FIG. 7(b) corresponds to the plane SK in FIG. To obtain a tomographic image of plane S,
What is necessary is to obtain projection data on the surface S. Therefore, consider projection data PI and P2 having the same projection angle β. Pl is the forward direction and P2 is the projection r-even when moving in the reverse direction. P.I.
, P2, the projection data P on the surface S is obtained. If projection data P(Lj) uses linear interpolation, P(+, j)=(PI(I, j)+pz(i,
J))/2...(force j=12...C
N CN: total number of channels j=1. 2. ...N
P NP: Find the total number of views. This process is O≦β
If it is performed for ≦180°, projection data for the first half-scan can be obtained. A desired tomographic image can be obtained by obtaining one tomographic image from the obtained 180° projection data, correcting this data fM and back projecting.

Incidentally, FIG. 9 shows a diagram corresponding to FIG. 6 in this second embodiment. In Example 2, one tomographic image was obtained from the obtained 180° projection data. However, as a third embodiment, a method for obtaining 360° projection data and obtaining a tomographic image will be described.

In FIG. 10, in order to obtain projection data for 360°, scanning of 360° is required in both forward and reverse directions. If the range t of the second embodiment is oo to 180 degrees, then in the third embodiment, scanning is required in the range of -90 degrees to 280 degrees. The first half scan is obtained in the same manner as in Example 2, and the second half scan is calculated using Q 1 (n) and Q'2 ( shown in FIG. 10(A)).
Q (fi) is similarly obtained from n), and one tomographic image can be reconstructed from all the obtained projection data. However, in Embodiment 3, if the latter half-scanning is required, the projection data used for interpolation will be far away, and the error due to interpolation will be larger than when calculating the first half-scanning. It won't happen.

FIG. 11 shows a control system diagram of the present invention. X-ray control unit 10
1 is a so-called xH explosion control which controls the high voltage generator 110 to generate high voltage.

The rotating frame control unit 102 not only controls the continuous rotation of the X-ray tube device (X-ray generator) and the X-ray detector while facing each other, but also controls the projection angle, and can arbitrarily control the projection angle. can be controlled.

Bed movement control section 103 controls bed movement direction and speed. However, the speed is constant during scanning.

The synchronization device 100 in the system control unit uses the position information from the ped position detector 113 and the projection angle information from the projection angle detector 114 to 103 synchronization.

Specifically, in Examples 2 and 3, the prespecified slice position is
=1. pp) -18), the scanning start position X is determined. However, D is determined by the bed movement speed and the rotation speed of the rotating frame. Position X at the end of forward scanning and projection angle θ
6 is memorized and the system is controlled so that the starting position of the backward scan is Xe and the starting projection angle is θ, +180'.

In the third generation (R-R method) CT system, algorithms for reconstructing tomographic images from projection data include a direct method in which the detected fan beam data is back-projected as is, and a parallel beam projection method in which the fan beam data is The Allen method, which converts data into data and then back-projects it, is known, but the present invention is effective regardless of the algorithm or generation.

According to this embodiment, continuous scanning can be performed simply by moving the patient ped, and high-speed continuous scanning is possible. Therefore, it is possible to save time when performing a cardiac skewer scan in which the heart is the object of imaging.
Lost time when performing dynamic scans of the liver, brain, etc. can be eliminated, and moreover, the imaging time can be shortened.

This has the effect of improving patient throughput.

Note that as an interpolation method, in addition to linear interpolation, high-level interpolation such as quadratic or cubic interpolation is also possible.

〔Effect of the invention〕

According to the present invention, continuous scanning is performed on the measurement site of the subject, and projection data on a tomographic plane can be obtained from the spiral data thus obtained.

[Brief explanation of drawings]

1. Fig. 1 is an embodiment of the uninvented CT device, and Fig. 2 is an R-
3 is an explanatory diagram of the continuous scan of the present invention, FIG. 4 (a) and (b) are explanatory diagrams of the spiral scan of the present invention, and FIG. Figure 6 is a diagram of the relationship between the rotational position and helical data, Figure 6 is a diagram of the relationship between the position and projection number, and Figure 7 is a diagram of the relationship between the position and projection number.
Figures (A) and (B) and Figures 8 (A) and (B) are explanatory diagrams of the second embodiment of the present invention, and Figure 9 is the relationship between the position and projection number in the second embodiment. FIGS. 1A and 1B are explanatory diagrams of a third embodiment of the present invention, and FIG. 11 is a control system diagram of the present invention. 1...X-ray tube device, 2...X-ray detector.

Claims (1)

[Claims] 1. An X-ray tube device that generates X-rays, an X-ray detector that is provided in opposition to the X-ray tube device and detects the X-rays that have passed through a subject, and an X-ray tube. It consists of a frame that carries the equipment and an X-ray detector and rotates continuously, and a bed on which the subject is placed and moves. An X-ray CT device that is moved in synchronization with the bed, and in the process of moving the bed, an X-ray tube device irradiates the subject with X-rays to perform a spiral scan. 2. The X-ray CT apparatus according to claim 1, wherein the bed moves in one direction. 3. The X-ray CT apparatus according to claim 1, wherein the bed is moved in a reciprocating manner. 4. An X-ray tube device that generates X-rays, an X-ray detector that is installed opposite to the X-ray tube device and detects the X-rays that have passed through the subject, and the X-ray tube device and the X-ray detector. The system consists of a frame that rotates continuously and a bed that carries a subject and moves in synchronization with the rotation of the X-ray tube device in a direction perpendicular to the rotation plane of the X-ray tube device. , in an X-ray CT apparatus configured to perform a helical scan by exposing the subject to X-rays from an X-ray tube device during the movement of the bed, the helical data obtained by the helical scan A buffer memory that stores SR according to an address determined by a projection number (position) and a scanner rotation number, an interpolation circuit that interpolates the spiral data SR in the memory to obtain projection data R, and a projection that is the output of the interpolation circuit. An X-ray device consisting of a back projection calculation circuit that back projects data and reconstructs images.